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CS 162Discussion Section

Week 1 (9/9 – 9/13)

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Who am I?

Kevin Kluescs162-ta@inst.eecs.berkeley.eduhttp://www.cs.berkeley.edu/~klueska

Office Hours: 12:30pm-2:30pm Mondays @ Soda 7th Floor Alcove

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Administrivia…• No electronics in section please!• Register on Piazza!• Possible short Quizzes in Section every week (part of your overall quiz grade for the course)• Start getting to know Nachos and setting up your

environment (links on course website)• Group Signup by 9/12 11:59 PM (This Thursday!)• All project members MUST attend same

discussion section!!

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Today’s Section

• Project Overview and Questions (10 min)• Sample Quiz (ungraded) (5 min)• Review Lectures 1 and 2 (20 min)• Worksheet and Discussion (15 min)

Project Goals

• Learn to work in teams • Use good engineering practices

– Version control, collaboration– Requirements specification– Design Document– Implementation – Testing– [Performance, reliability, ...] analysis

• Understand lecture concepts at the implementation level

Project Grading

• Design docs [40 points]– First draft [10 points]– Design review [10 points]– Final design doc [20 points]

• Code [60 points]

Good Project Lifetime

• Day 0: Project released on course webpage • Day 1 13: Team meets, discusses and breaks up work on ‐

design and necessary prototyping • Day 14: Initial design document due

– Team reviews the document with TA • Day 15: Implementation begins • Day 20: Implementation is finished. Team switches to

writing test cases. Design doc has been updated to reflect the implementation.

• Day 21: Iteration and performance analysis. • Day 23: Team puts finishing touches on write up and gets

to bed early.

Project 1: Thread Programming

Project 2: Multiprogramming

Project 3: Key Value Store

Key Value Store API

Application

Key 1 Value 1

Key 2 Value 2

Key 3 Value 3

Key 4 Value 4

Project 4: Distributed KV Store

Key Value Store API

Application

Key 1 Value 1

Key 1 Value 1

Key 1 Value 1

Version Control for the Projects

• Course provided SVN and Private GitHub repos for every group

• Use whichever you prefer

• Access:svn: https://void.eecs.berkeley.edu/cs162/groupXXgit: https://github.com/Berkeley-CS162/groupXX

Project Questions?

Sample Quiz

1. (True/False) Threads within the same process share the same heap and stack.

2. (True/False) Preemptive multithreading requires threads to give up the CPU using the yield() system call.

3. (True/False) Despite the overhead of context switching, multithreading can provide speed-up even on a single-core cpu.

4. What is the OS data structure that represents a running process (i.e. holds its current state)?

5. What is the mechanism by which different processes communicate with one another called?

What is an OS and What does it do?

A computer boot sequence

Hardware

Operating System

Memory Mgmt

File Systems Scheduler ….

BIOS

Boot LoaderNetworks

Application Application Application Application

T1 T2

T3 T4

Why do you want an OS?

• Isolation– Fault: “if my program crashes yours shouldn’t” – Performance: “if my program starts to do some massive

computation, it shouldn’t starve yours from running”• Mediation (multiplexing/sharing + protection)

– Manage the sharing of hardware resources (CPU, NIC, RAM, disk, keyboard, sound card, etc)

• Abstractions and Primitives– Set of constructs and well defined interfaces to simplify application ‐

development: “all the code you didn’t write” in order to implement your application

• Because hardware changes faster than applications! • Because some concepts are useful across applications

Benefits of having an OS?

• User benefits – Efficiency (cost and performance)

• Share one computer across many users• Concurrent execution of multiple programs

– Safety• OS protects programs from each other• OS fairly multiplexes resources across programs

• Application benefits– Simplicity

• Sockets instead of ethernet cards

– Portability• Device independence: tiCOM card or Intel card?

Why is concurrency hard?

What do you need to get concurrency working?

Concurrency

• Concurrency means multiple threads of computation can make progress, but possibly by sharing the same processor– Like doing homework while chatting on IM

• Why Concurrency?– Consider a web server: while it’s waiting for a response

from one client, it could read a request for another client – Consider a browser: while it’s waiting for a response from a

web server, it wants to react to mouse or keyboard input Concurrency increases/enables responsiveness

Different levels of abstraction

• Threads• Processes• Symmetric multithreading• Distributed systems (Single system image)

What is a thread?

A thread of execution is the smallest unit of processing that can be scheduled by an operating system. – Wikipedia circa Jan ‘12

What resources does a thread have?

Single and Multi Threading

What is the difference between a

Thread and a Process?

What is a Process?

Process ControlBlock

Process Address Space

Pro

gram

Ad

dress S

pace

What is an address space?

What does this mean in terms of hardware?

Operating System Memory Management

Prog 1Virtual

AddressSpace 1

Prog 2Virtual

AddressSpace 2

Code

Data

Heap

Stack

Code

Data

Heap

Stack

Data 2

Stack 1

Heap 1

OS heap & Stacks

Code 1

Stack 2

Data 1

Heap 2

Code 2

OS code

OS dataTranslation Map 1 Translation Map 2

Physical Address Space

When and how do you switch between processes?

Scheduling states

Context Switching

FetchExec

R0…

R31F0…

F30PC

…Data1Data0

Inst237Inst236

…Inst5Inst4Inst3Inst2Inst1Inst0

Addr 0

Addr 232-1

Recall (61C): What happens during execution?

• Execution sequence:– Fetch Instruction at PC – Decode– Execute (possibly using registers)– Write results to registers/mem– PC = Next Instruction(PC)– Repeat

PCPCPCPC

Questions about the course?

Workseet…